Veneer clippers of various types have been proposed which are adapted to cut successively sheets of wood veneer for producing sized veneer sheets each having a predetermined length and width and also for eliminating defective portions of each incoming veneer sheet such as irregularly-shaped leading and trailing edges, cracks, splits and other open defects to yield usable veneer sheets each having a rectangular shape. A veneer clipper which is designed specifically to make successive cuts continuously while a veneer sheet is being moved without a stop through the clipper is disclosed by U.S. Pat. No. 4,008,639 which is assigned to the same assignee as the present invention.
This clipper includes a pair of rotatable anvil rolls disposed one above the other with their axes extending in parallel to each other and positioned to provide a nip therebetween, a feeding conveyer for advancing a veneer sheet toward the nip, and a clipper knife having a straight cutting edge and carried on a holder positioned downstream of the nip. The knife holder is adapted to pivot alternately in opposite directions about an axis parallel to those of the anvil rolls thereby to cause the knife to cut into veneer sheet each time its holder pivots in either direction. In this veneer clipper, veneer cutting is accomplished by the aid of a force by which the veneer sheet is advanced through the nip and the cutting is effected at a position on the sheet which has been determined by a plurality of veneer thickness detectors arranged on the upstream side of the anvil rolls. This clipper has made possible speedy and efficient clipping operation because the veneer sheet does not have to be stopped temporarily for each cut and trims of defective portions cut off from the sheet can be removed and discharged smoothly from the cutting area, thus contributing greatly to the improvement of clipping operation in a veneer processing line.
In the above veneer clipper having a knife with conventional arrangement wherein its cutting edge extends straight and parallel to the axis of the anvil rolls, the entire length of the knife edge cuts into the veneer sheet simultaneously and, therefore, each roll will receive at the same time all the cutting force required for each cut. The anvil roll thus subjected to the cutting force tends to bend or bow away from the knife which then cuts into the veneer sheet and such bending or bowing of the anvil roll causes an incomplete cut. Though this roll bending can be prevented by making the rolls larger in diameter to provide a rigidity that is great enough to resist the bending, it is difficult to cut a veneer sheet successfully on such rolls due to the fact that the angle formed between the knife and an imaginary tangential line at the point of contact of the knife edge with the periphery of such large-diameter roll becomes too acute for proper cutting. Thus, It is desirable that an anvil roll should be small in diameter to make the above angle as close to right angle as possible, but large enough to resist the bending force created during cutting. It is noted that the above bowing of the anvil rolls takes place more easily as the rolls become longer or when the length along which a veneer sheet is cut becomes greater.